The supported highly active and highly stereospecific catalysts for the polymerization of propylene and higher olefins known up to now are obtained by the reaction of an Al alkyl compound partially complexed with an electron-donor compound (outside donor) with a solid component comprising a Ti compound and an electron-donor compound (inside donor) supported on a Mg dihalide in active form.
Examples of such catalysts have been described in British Patent No. 1,559,194 and Belgian Patent No. 868,682.
Those supported catalysts require the use of an inside donor in order to obtain polymers having a high isotactic index. If the inside donor is omitted, polymers having a low isotactic index are obtained.
One object of this invention is to provide catalyst components which comprise a silicon compound as defined herein-above and which yield catalysts that polymerize the alpha-olefins to high yields of polymers having a high isotacticity index.
This and other objects are achieved by the present invention in accordance with which it has been found, unexpectedly, that it is possible to obtain, with high yield, polymers of alpha-olefins having a high isotactic index by using Ti-containing Mg dihalides-supported catalysts free from inside electron-donor compounds, if an outside donor is used which is a silicon compound containing Sixe2x80x94OR, Sixe2x80x94OCOR or Sixe2x80x94NR2 bonds.
It has also been found,even more unexpectedly, that the activity and stereospecificity of the catalysts can be further increased if the silicon compound used as outside donor is present as inside donor also in the Ti-containing Mg dihalide-supported component in amounts corresponding to molar ratios between the silicon compound and the supported halogenated Ti- compound comprised between 0.1 and 5.
The above results are surprising if one considers that catalysts are known which are prepared by using, as both inside and outside donor, a silicon compound containing Sixe2x80x94Oxe2x80x94C bonds and the activity and stereospecificity of which are not increased over the activity and stereospecificity obtainable with catalysts in which an ester of benzoic acid is used as inside and outside donor.
The catalysts of this invention comprise the product of the reaction between the following components:
(a) an Al trialkyl or Al alkyl compound containing 2 or more aluminum atoms linked to each other through oxygen or nitrogen atoms or through SO4 or SO3 groups;
(b) a silicon compound containing one or more Sixe2x80x94OR, Sixe2x80x94OCOR or Sixe2x80x94NR2 bonds (R being a hydrocarbyl radical); and
(c) a solid comprising, as essential support, an anhydrous Mg dihalide in the active form as defined infra and, supported on said dihalide, a Ti halide or Ti haloalcoholate, or the solid (c) containing supported therein also a silicon compound as defined in (b) in an amount corresponding to a molar ratio between the supported silicon compound and the supported halogenated Ti compound comprised between 0.1 and 5.
The active anhydrous Mg dihalides forming the essential support of component (c) are the Mg dihalides showing in the X-rays powder spectrum of component (c) a broadening of at least 30% of the most intense diffraction line which appears in the powder spectrum of the corresponding dihalide having 1 m2/g of surface area, or are the Mg dihalides showing an X-rays powder spectrum in which said most intense diffraction line is replaced by a halo with the intensity peak shifted with respect to the interplanar distance of the most intense line; and/or are the Mg dihalides having a surface area greater than 3 m2/g.
The measurement of the surface area of the Mg dihalides is made on component (c) after treatment with boiling TiCl4 for 2 hours. The found value is considered as surface area of the Mg dihalide.
Very active forms of Mg dihalides are those giving an X-rays powder spectrum in which the most intense diffraction line appearing in the spectrum of the corresponding halide having 1 m2/g of surface area is decreased in relative intensity and broadened to form a halo, or are those in which said most intense line is replaced by a halo having its intensity peak shifted with respect to the interplanar distance of the most intense line. Generally, the surface area of the above forms is higher than 30-40 m2/g and is comprised in particular between 100-300 m2/g.
Active forms are also those deriving from the above forms by heat-treatment in inert hydrocarbon solvents and showing, in the X-rays spectrum, sharp diffraction lines in place of the halos.
The sharp, most intense line of these forms shows a broadening of at least 30% with respect to the corresponding line of the Mg dihalide having 1 m2/g of surface area.
Preferred Mg dihalides are Mg dichloride and Mg dibromide. The content in water of the dihalides is generally less than 1% by weight.
By Ti halides or Ti haloalcoholates and esters supported on the active Mg dihalide is meant the above compound which may be chemically or physically fixed on the support, and not extractable from component (c) by treatment of the same with boiling 1,2-dichloroethane for 2 hours.
Components (a), (b) and (c) are made to react with each other in any order; preferably, however, components (a) and (b) are premixed before being contacted with component (c).
The pre-mixing of (a) and (b) is conducted at temperatures comprised, usually, between room temperature and the temperature used in the polymerization process.
The pre-reaction of (c) and (b) may be carried out also at higher temperatures. Also, compound (b) may be incorporated and made to react with component (c) itself. Component (b) is made to react in a molar ratio with respect to the halogenated Ti compound supported on component (c) of at least 1 and in a molar ratio with respect to the Al alkyl compound used as component (a) of less than 20 and preferably comprised between 0.05 and 0.3.
In component (c), the molar ratio between the Mg dihalide and the halogenated Ti compound supported therein is comprised between 1 and 500 and the molar ratio between said halogenated Ti compound and the electron-donor supported on the Mg dihalide is comprised between 0.1 and 50.
The silicon compounds set forth in (b) include compounds of general formula:
RmSiYnXp
wherein:
R is an alkyl, alkenyl, aryl, arylalkyl or cycloalkyl radical with from 1 to 20 carbon atoms;
Y is an xe2x80x94ORxe2x80x2, xe2x80x94OCORxe2x80x2, xe2x80x94NRxe2x80x22 group wherein Rxe2x80x2, either equal to or different from R, has the same meaning as R;
X is either a halogen or hydrogen atom or an xe2x80x94OCORxe2x80x3 or xe2x80x94NRxe2x80x32 group wherein Rxe2x80x3, either equal to or different from Rxe2x80x2, has the same meaning as Rxe2x80x2;
m, n and p are numbers comprised, respectively, between: 0 and 3 for m, 1 and 4 for n and 0 and 1 for p; and m+n+p is equal to 4.
Other silicon compounds that may be used are compound in which two or more silicon atoms are bound to each other through oxygen or nitrogen atoms.
Examples of these compounds are hexaethoxydisiloxane and symmetrical diphenyltetraethoxydisiloxane: 
Preferred silicon compounds are: phenylalkoxysilanes such as phenyltriethoxy or trimethoxysilane, diphenyldimethoxy and diethoxysilane, monochlorophenyldiethoxysilane; alkylalkoxysilanes as, e.g., ethyltriethoxysilane and ethyltriisopropoxysilane.
Examples of other suitable compounds are: chlorotriethoxysilane, acetoxytriethoxysilane, vinyltriethoxysilane, butyltriethoxysilane, triphenylmonoethoxysilane, phenyltricycloethoxysilane, phenyldiethoxydiethylaminosilane, tetraphenoxysilane and tetralkoxysilanes such as tetramethoxysilane.
The silicon compound can be also formed in situ by reaction of, for instance, a halogenated silicon compound such as SiCl4 with an alcohol or an alcoholate of Mg or Al.
In the catalysts of the invention the silicon compound is present in a combined form in the solid product of the reaction between the various catalyst-forming components, in a molar ratio between the silicon compound and the halogenated Ti compound greater than 0.05 and generally comprised between 0.1 and 5.
The Al alkyl compounds forming component (a) include Al trialkyls as, for instance, Al triethyl, Al triisobutyl, Al triisopropyl, and compounds containing two or more Al atoms linked to each other through hetero-atoms as:
(C2H5)2Alxe2x80x94Oxe2x80x94Al(C2H5)2, 

and 
As indicated, Al alkyl compounds in which Al atoms are linked through groups such as SO4 or SO3 are also suitable.
The Al alkyl compounds may be used in mixture with Al alkyl halides, e.g., AlEt2Cl.
Component (c) is prepared according to various methods, one of which, and also one of the preferred methods, consists in co-milling the Mg dihalide, the Ti halide or Ti haloalcoholate and the silicon compound when it is used, until appearance in the X-rays spectrum of the milled product of the modifications above set forth for the spectrum of the Mg dihalide and in heat-treating the milled product in suspension in a halogenated hydrocarbon as, e.g., 1,2 dichloroethane, separating the solid product and washing it with heptane or a similar hydrocarbon solvent. The duration of the treatment is generally comprised between 1 and 4 hours and depends on the temperature of treatment.
According to another method, an adduct between a Mg dihalide and an alcohol is reacted with TiCl4. The reactions are described in Belgian patent 868,682 and published German patent No. 3,022,738.
In all the above methods, the final product contains a Mg dihalide, present in the active form as set forth supra.
Other known methods which lead to the formation of Mg dihalide in active form or to Ti-containing Mg dihalide supported components, in which the dihalide is present in active form, are based on the following reactions:
reaction of a Grignard reagent or a MgR2 compound (R being a hydrocarbyl radical) or complexes of said MgR2 compounds with Al trialkyls, with halogenating agents as AlX3 or AlRmXn compounds (X is halogen, R is a hydrocarbyl, m+n=3 SiCl4 or HSiCl3;
reaction of a Grignard reagent with a silanol or polysiloxane, H2O or with an alcohol and further reaction with a halogenating agent, or with TiCl4;
reaction of Mg with an alcohol and a halogenhydric acid, or of Mg with a hydrocarbyl halide and an alcohol;
reaction of MgO with Cl2 or AlCl3;
reaction of MgX2.nH2O (X=halogen) with a halogenating agent or TiCl4;
reaction of Mg mono or dialcoholates or Mg carboxylates with a halogenating agent.
The Ti halides or Ti halogenalcoholates include, in particular, the Ti tetrahalides, Ti trihalides and Ti trihalogenalcoholates. Preferred compounds are: TiCl4, TiBr4, 2,6-dimethylphenoxytrichlorotitanium.
The Ti trihalides are obtained according to known methods, for instance by reduction of TiCl4 with Al or an organometallic Al compound or with hydrogen.
In the case of Ti trihalides, it may be convenient, for the purpose of improving the performance of the catalysts, to carry out an oxidization, even if partial, of the titanium, either during or after the preparation of component (c). To this purpose there may be used halogens, iodine halides.
Preferred catalysts are those in which: component (c) is obtained from MgCl2, TiCl4 a silicon compound selected from the groups of phenyl or ethyltriethoxysilane or diphenyldimethoxy or diethoxysilane, and
Component (a) is an Al trialkyl, such as Al triethyl or Al triisobutyl.
One of the preferred methods of preparing component (c) consists in co-milling MgCl2, TiCl4 and the silicon compound and in treating the milled product with a halogenated hydrocarbon such as, for instance, 1,2-dichloroethane.
The catalysts according to this invention are used to polymerize the alpha-olefins according to known methods, that is, by carrying out the polymerization in a liquid phase, either in the presence or absence of an inert hydrocarbon solvent, or in gas phase or by combining, for instance, a liquid phase polymerization step with a gas phase step.
In general, the polymerization temperature is comprised between 40xc2x0 and 160xc2x0 C., but preferably between 60xc2x0 and 90xc2x0 C., operating either at atmospheric or at greater than atmospheric pressure.
As a molecular weight regulator hydrogen or other regulators of known type are used.
The catalysts are particularly suitable for polymerizing propylene, butene-1, styrene and 4-methylpentene. The catalysts may also be used according to known methods to polymerize mixtures of propylene and ethylene to form modified polypropylenes having improved shock-resistance at low temperatures (the so called block copolymers of propylene and ethylene) or to obtain random crystalline copolymers of propylene with minor proportions of ethylene.